Chapter 9 - Statsby

In a sample of 18 participants, a researcher estimates the 80% CI for a sample with a mean of M1 - M2 = 8.8 and an estimated standard error for the difference (mc008-1.jpg) of 1.8. What is the lower confidence limit for this interval?

6.4

In a sample of 14 participants, a researcher estimates the 90% CI for a sample with a mean of M1 - M2 = 10.7 and an estimated standard error for the difference (mc001-1.jpg) of 2.9. What is the confidence interval at this level of confidence?

90% CI 5.5, 15.9

In a sample of 30 participants, a researcher estimates the 95% CI for a sample with a mean of M1 - M2 = 0.7 and an estimated standard error for the difference (mc009-1.jpg) of 0.2. What is the confidence interval at this level of confidence?

95% CI 0.3, 1.1

Which measure of effect size is most commonly reported with a t test?

Cohen's d

A researcher records the crying time (in minutes) of infants given oral administration of sucrose (n = 12) or tap water (n = 16) prior to a heel prick. The mean crying time in the sucrose group was 3.3 ± 2.4 (M ± SD) min; in the tap water group, it was 7.3 ± 1.6 (M ± SD) min. If the null hypothesis is that there is no difference in crying time, then what is the decision for this test?

Crying time was significantly reduced among infants given the sucrose solution prior to a heel prick.

A professor teaches a certain section of material using a lot of examples with sports and cars to illustrate. He is concerned that this may have biased his instruction to favor male students. To test this, he measures exam grades from this section of material among women (n = 10) and men (n = 10). The mean score in the male group was 84 ± 4.0 (M ± SD); in the female group, it was 78 ± 8.0 (M ± SD) points. If the null hypothesis is that there is no difference in exam scores, then test the null hypothesis at a .05 level of significance for a two-tailed test.

Exam scores were significantly higher in the male group, t(18) = 2.12, p < .05.

Which figure below depicts data from a study on child play behavior with a smaller value for error variance? (Tables shown)

Figure A

Is a one-sample t test reported differently for one-tailed and two-tailed tests?

No, the same values are reported.

A researcher has participants rate the likability of a sexually promiscuous person described in a vignette as being male (n = 20) or female (n = 12). The mean likability ratings in each group were 4.0. If the null hypothesis is that there is no difference in likability ratings, then do likability ratings differ at a .05 level of significance?

No, this result is not significant, t(30) = 0.

A researcher finds that the mean difference in productivity between employees working the morning shift (n = 16) and the night shift (n = 10) is 5.0 units, and the estimated standard error for the difference is 2.7 units. If the null hypothesis states that there is no difference in productivity, then is this result significant at a .05 level of significance for a two-tailed test?

No, this result is not significant.

Two researchers (A and B) compute a two-independent-sample t test. For both tests, the mean difference between the two groups is 10, but the standard error is smaller for Researcher A. Which test is more likely to result in a decision to reject the null hypothesis?

Researcher A

Two researchers (A and B) compute a two-independent-sample t test. For both tests, the standard error is the same, but the mean difference between the groups is larger for Researcher A. Which test is more likely to result in a decision to reject the null hypothesis?

Researcher A

A researcher conducts two t tests. Test 1 is a two-tailed test with a smaller sample size at a .05 level of significance. Test 2 is a two-tailed test with a larger sample size at a .05 level of significance. What do you know about the degrees of freedom for each test?

Test 2 is associated with larger degrees of freedom.

A researcher conducts two t tests. Test 1 is a one-tailed test with a smaller sample size at a .05 level of significance. Test 2 is a one-tailed test with a larger sample size at a .05 level of significance. What do you know about the critical values for each test?

Test 2 is associated with smaller critical values.

A researcher reports that the mean difference in the body weight of rats following a pharmacological versus control treatment is 14 g, with a pooled sample variance equal to 256. What is the effect size for this test using estimated Cohen's d?

d = 0.88; large effect size

The more that scores in each group ______, the larger the error variance.

overlap

The less that scores overlap between groups, the ______ the error variance.

smaller

Which of the following summarizes a t test that was significant and associated with a large effect size?

t(12) = 2.95, p < .05, d = .82

To compute a two-independent-sample t test, a researcher has to know many values. Which of the following is not a value that the researcher must know to compute this test?

the pooled population variance

As a requirement for the t test, researchers compute any type of t test with samples selected from populations in which ______.

the population variance is unknown

A researcher compares differences in mean health scores between students at two local high schools. Assuming that the population variance is unknown, what type of t test is appropriate for this study?

two-independent-sample t test

A researcher conducts a study measuring differences in brain activity among rats placed on either a continuous or intermittent reward schedule. Assuming that the population variance in unknown, what t test is appropriate for this study?

two-independent-sample t test

A researcher records differences in ratings of emotion among participants watching either a drama or a romance film. Assuming that the population variance is unknown, what type of t test is appropriate for this study?

two-independent-sample t test

State the critical value(s) for a t test using a .05 level of significance in the lower tail only: t(24).

~1.711

State the critical value(s) for a t test using a two-tailed test at a .05 level of significance: t(20).

±2.086

A researcher selects a sample of 32 participants who are assigned to participate in a study with one group. What are the degrees of freedom for this test?

31

In a sample of 18 participants, a researcher estimates the 80% CI for a sample with a mean of M1 - M2 = 8.8 and an estimated standard error for the difference (mc007-1.jpg) of 1.8. What is the upper confidence limit for this interval?

11.2

A researcher reports that the effectiveness of a new marketing campaign significantly increased sales compared with the previous campaign strategy, t(49) = 2.562, p < .05. Use eta-squared to interpret the effect size for this result.

12% of the variability in marketing effectiveness can be accounted for by the new marketing strategy.

A researcher reports that the mean difference in response time to an auditory versus a visual cue is 0.83 s, with a pooled sample variance equal to 2.45. What is the effect size for this test using estimated Cohen's d?

d = 0.53; medium effect size

Which of the following is an assumption for the two-independent sample t test, but not the one-sample t test?

equal variances

Which type of error is used to compute the confidence interval for two independent samples selected from at least one population with an unknown variance?

estimated standard error for the difference

A researcher reports a significant mean difference in a given population. If she computes both eta-squared and omega-squared to measure the effect size, then which estimate will be the most conservative?

omega-squared

Eta-squared is computed ______ for the one-sample, and the two-independent-sample t tests.

similarly

A researcher reports that stress levels among nurses are higher compared to stress levels in the general population, t(20) = 2.086, p = .05 (d = .12). Was this a one-tailed or a two-tailed test?

Two-tailed test because the p value is equal to .05.

Computing a two-independent-sample t test is appropriate when ______.

all of these

Which of the following is an assumption for computing any type of independent sample t test?

all of these

A research design in which different participants are observed one time in each group of a research study is called ______.

between-subjects design

A type of factor in which different participants are observed in each group, or at each level of the factor, is called ______.

between-subjects factor

State the critical value(s) for the following two-tailed t test at a .05 level of significance: t(mc006-1.jpg).

both B and C